Christians who travel to a major pilgrimage center often return home with a small memento like a medallion, or a badge. This tradition finds its basis in the belief that an object that comes from a holy place retains the sanctity of its origins.

The practice of collecting mementos, or eulogiai, associated with a holy place began some time in the fourth century, when pilgrims first made their way to Jerusalem. One of their most coveted items was a piece of the True Cross, reportedly discovered by Saint Helena, the mother of Constantine the Great. However, only the most well connected pilgrims were able to attain such a prize, with most having to settle for flasks of oil that had come into contact with the wood of the cross.

Indeed, the trade in relics, as it developed over the course of the Middle Ages, is indicative of contemporary social hierarchies. Thus, the emperor was able to collect some of the most important relics for his palace chapel in Constantinople, including the lance that was reportedly pierced Christ's side during his crucifixion, but so could the pope.

Pope Gregory the Great made this clear when he refused to give the head of Saint Paul to the Empress Constantina, wife of the Emperor Saint Maurice, citing the ancient prohibition against bodily dismemberment. Of course, the popes had no problem receiving parts of saints's bodies as gifts, as evidenced by the contents of the Sancta Sanctorum, located in the Basilica of St. John Lateran.

Dedicated to Saint Lawrence, the Sancta Sanctorum, served as the private chapel of the popes for centuries, and to this day contains some of the most venerated relics in Christendom, including an achaeiropoietos—a term used to describe an image not made by human hands—that depicts Christ.